6 Answers
6

Originally the briefcase contained diamonds. But that just seemed too
boring and predictable. So it was decided that the contents of the
briefcase were never to be seen. This way each audience member would
fill in the blank with their own ultimate contents. All you were
supposed to know was that it was "so beautiful." No prop master can
come up with something better than each individual's imagination. At
least that was the original idea. Then somebody had the bright idea
(which I think was a mistake) of putting an orange lightbulb in there.
Suddenly what could have been anything became anything supernatural.
Didn't need to push the effect. People would have debated it for
years anyway, and it would have been much more subtle. I can't
believe I'm actually talking about being subtle.

This was verified by Tarantino when he was directly asked at ComicCon in San Diego by an audience member. His quote was, "What do you think was in the briefcase? Because by asking yourself that, you make your own unique version of the film for yourself."
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Andrei FreemanJan 31 '12 at 14:57

What's really strange here is that Ebert implies it is supernatural because of the light bulb. I always thought it was just a briefcase that happened to light up when you open in. You know, like some briefcases are rigged to do.
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JoshDMSep 9 '13 at 20:41

That's a cop-out by Tarantino. He has already gone on record years ago to say that it was supposed to be Wallace's soul. He has every right to change his mind, but that is why you see a Band-Aid clearly on the back of Wallace's neck--in folklore that is where the "devil" steals your soul.
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sss4rJul 10 at 1:55

Well people try and make tenuous Links between reservoir dogs and pulp fiction, by that I mean people try and see if they hold up as sequels, whether continuity wise they can work. A logical opinion is to say that the diamonds that are stolen in Dogs are what are in the brief case in Fiction. However Harvey Keitel and Quentin Tarantino act as two different people in both films. So this still doesn't hold true. I heard a theory that it was Wallaces soul that was in the case. Evidence for this is that losing his soul is what the injury on the back of his neck is. However that seems far fetched.

I agree and even though Pulp is "Ultra Violent", it's not far fetched!
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benhowdle89Dec 1 '11 at 9:36

Well even though it is silly, it's possible that actors can "act" as two different people and still be in the same "movie world." An example of that is in "Jay and Silent Bob" strike back" where Jason Lee plays two different characters from two different movies, as well as Ben Aflec referring to himself. I do believe you are correct though about individuals trying to hold up continuity though, as I consider Pulp Fiction and Reservoir Dogs to be separate.
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5StringRyanDec 9 '11 at 16:55

I've always assumed (despite Avary's explanation) that it was a clever movie reference to the McGuffins in two previous movies.

The most recent being the great Repo Man (Dir Alex Cox, 1984) where a briefcase purported to contain alien remains and which glows mysteriously is a key thread. This, in turn, may have some relationship with the case of radioactive material in the great noir thriller Kiss Me Deadly (Dir Robert Aldrich, 1955).

If you are going to include references to other movies (a known Tarantino trait) those are two awesome movies to reference.

I heard the theory that @JosephLynn mentioned about it being Wallace's soul - and relating it to the injury on the back of his neck. The theory only has slim backing - the glow, the band-aid, the combination of the briefcase (666) and the 'miracle' that happens as Vince and Jules come to take the soul back, perhaps rescuing it from the devil.

Obviously the quote from Avery saying that they didn't have a fixed idea of what it was kind of trumps that.

Until reading the other answers here I always assumes that it contained gold bars because of the orange glow. I know this is a slightly boring conclusion but I don't think that Pulp Fiction is supernatural in any way and the theory about Wallace's soul is just silly.

It had to be something very valuable due to Tim Roth's reaction to it and the colour of the glow makes me think gold rather than diamonds.

I'm afraid I must also weigh in with boring old, run of the mill diamonds. I read that Tarantino didn't want to use diamonds (even though that's what is in the briefcase according to the script) because he'd just come off Reservoir Dogs which featured a diamond heist.